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Solved Bed Heater problem - probably Marlin 1.14 related

Discussion in 'Troubleshooting' started by Robert55, Jul 28, 2017.

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  1. Robert55

    Robert55 Member

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    I've got a bit of a problem since updating to Marlin 1.14. Surprisingly, the ABL works. However, as shown in the attached video, when I turn the bed heat on, it just takes off and doesn't stop. Period. Even when it hits MaxTemp. The LCD controller says it's been shut down at 150C, but it got up to 188C before I manually turned it off. Thermistor is fine (I'm getting a good reading). Solid State Relay is fine - it's doing it's job. But once the heat signal comes from the mainboard, it does-not-turn-off. Period. Bad problem to have. Thanks. https://www.dropbox.com/s/dum85hkn9rml3bx/20170728_221114.mp4?dl=0
     
  2. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Mad MOSFET on RAMPS board... Q3

    That is the most likely suspect.
     
  3. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    I meant to type BAD but MAD works
     
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  4. Robert55

    Robert55 Member

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    Any way to check the MOSFET?? There isn't really any current going through it anymore - all it does is energize the SSR, which it can do with 3 volts.. It was working before the firmware upgrade.

    Nevermind - found a youtube video right away. I'll be back....lol
     
  5. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    If you think it is firmware related drop back to stock Marlin.
    I doubt that is it, but easy to test
     
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  6. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    A MOSFET is a switch. Sounds like yours is stuck ON
     
  7. Robert55

    Robert55 Member

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    Will do. Right now, my CR-10 is hogging the laptop. I used my spare MEGA2560 to burn a bootloader to it yesterday, and flashed 1.14 to that one. Now the mainboard only wants to be powered through the USB only...(sigh)
     
  8. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    The Q3 part failing is, sadly, fairly common. That is why I usually suspect it first. Let us know how it goes.
     
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  9. Robert55

    Robert55 Member

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    At least I have a spare board....right now it's flashed as a programmer, but that's easily corrected. You need jumper cables to burn a bootloader to the CR-10 board, but it runs its own flavor of Marlin fine.
     
  10. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    It is the ramps that has the problem and there is no firmware on that. The arduino is probably fine.

    Sent from my SAMSUNG-SM-G930A using Tapatalk
     
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  11. Robert55

    Robert55 Member

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    Got one of those too.Thanks.

    Sent from my LGLS996 using Tapatalk
     
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  12. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    Nothing has changed in the way bed heaters are handled in 1.1.4 so I highly doubt that is the cause.
     
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  13. Robert55

    Robert55 Member

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    I finished switching the RAMPS board, and when I looked at the old MOSFET, there were no obvious signs of failure. I have NOT taken a multimeter to it yet.

    I still find this highly unusual - it worked fine for quite awhile. I have an SSR sending actual power to the bed heater. The MOSFET only has to send a signal voltage to the SSR. Is there someplace in the firmware where I can limit the output voltage/current of the MOSFET?? If there is, I'd like to do that before I burn up another one.

    Also unusual - if the MOSFET had failed, a fresh boot-up of the board should either be immediate heating of the bed, or no heating at all. It turned on correctly, but would not turn off.
     
    #13 Robert55, Jul 29, 2017
    Last edited: Jul 29, 2017
  14. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    There is no way to control the RAMPS in software (other boards like Rambo offer this, but not the arduino/RAMPS)

    It happens and is not uncommon. Just a weak point in the RAMPS board. Generic ones are $15 (US) and if you have an R1+ I suggest you read the thread on swapping to a generic one :)

    Usually when the MOSFET dies there is no obvious sign of it. In rare cases they will smoke off, but that is not normal.
     
  15. Robert55

    Robert55 Member

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    That was it!!! I'm still a little wierded out by this one - I could understand if the bed heater was hooked up to it, but I put that SSR in there specifically to take a bunch of the load off the MOSFET. Weak point, indeed!!!

    Thanks a lot for the help, guys!!! We can close this threaded as "Resolved".
     
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